Time is running out and Rowena isn't getting anywhere with her translation of The Book of The Damned, because the codex Sam got for her to aid in the translation is, itself, encoded!
Sam calls in Charlie (Felicia Day) to employ her computer skills on cracking the codex code, and Castiel to watch over her and Rowena.
Meanwhile, Dean is getting very suspicious of Sam's evasive behaviour (Sam is a dreadful liar), but has found a case for them to work... which just happens to involve a member of the Styne family (who, you remember, are also looking for The Book Of The Damned).
We get the impression that the Styne aren't quite human, but when Sam and Dean capture Eldon Styne (David Hoflin), he reveals the full story of the family's bio-engineering talents which they use to enhance their kin (which is why they 'harvest' organs from their murder victims).
Eldon also explains that they are an ancient family, who have long been operating behind-the-scenes and profiting from mankind's darkest moments, but were forced to change their name when their skills were made public in the early 19th Century by a certain Mary Shelley.
For an instant, I was slightly underwhelmed by the introduction of the Frankenstein name into Supernatural, but then I quickly remembered they also gave us Oz a little ago and that gelled with the show's oeuvre, so why not Frankenstein?
But, of course, the biggest bombshell of the episode wasn't the revelation of the Frankensteins, but that brutal, bloody, final scene, marking the exit of a fan-favourite character from the Winchester's extended family.
Of course, we know from past experience, that - as in comics - death isn't always the end in Supernatural. But there was a slasher-flick starkness about that final shot that suggests that maybe this time it really is.
Next Time (massive spoilers from the get-go if you're not up to speed):